The present invention relates to the field of microwave thermal therapy of tissue, and in particular to a catheter for transurethral microwave thermal therapy of benign prostatic hyperplasia (BPH).
The prostate gland is a complex, chestnut shaped organ which encircles the urethra immediately below the bladder. Nearly one-third of the prostate tissue anterior to the urethra consists of fibromuscular tissue that is anatomically and functionally related to the urethra and bladder. The remaining two-thirds of the prostate is generally posterior to the urethra and consists of glandular tissue.
This relatively small organ, which is the most frequently diseased of all internal organs, is the site of a common affliction among older men: benign prostatic hyperplasia (BPH). BPH is a nonmalignant, bilateral nodular expansion of the prostate tissue in the transition zone, a periurethral region of the prostate between the fibromuscular tissue and the glandular tissue. The degree of nodular expansion within the transition zone tends to be greatest anterior and lateral to the urethra, relative to the posterior-most region of the urethra.
Left untreated, BPH causes obstruction of the urethra which can result in increased urinary frequency, urgency, incontinence, nocturia, and a slow or interrupted urinary stream. BPH may also result in more severe complications, such as urinary tract infection, acute urinary retention, hydronephrosis, and uraemia.
Traditionally, the most common treatment for BPH has been a surgical operation known as TURP (transurethral resection of the prostate). During TURP surgery, a portion of the healthy urethra is removed in order to gain access to the tumorous prostate tissue. A heated cauterizing scope is then inserted through the tip of the penis and into the urethra to remove the tumorous prostatic tissue. After the surgery, the patient is required to stay in the hospital for several days, wearing a catheter. TURP surgery, however, is often not an available method of treatment for a variety of reasons. First, due to the advanced age of many patients with BPH, other health problems such as cardiovascular disease can warrant against surgical intervention. Second, potential complications and side effects associated with transurethral surgery such as hemorrhaging, anesthetic complications, urinary infections, dysuria, incontinence, and retrograde ejaculation can adversely affect a patient's willingness to undergo such a procedure.
A fairly recent alternative method of treatment for BPH involves microwave thermal therapy, in which microwave energy is employed to elevate the temperature of tissue surrounding the prostatic urethra above about 45.degree. C., thereby thermally damaging the tumorous tissue. Delivery of microwave energy to tumorous prostatic tissue is generally accomplished by a microwave antenna-containing applicator positioned within a body cavity adjacent the prostate gland. The microwave antenna, when energized, heats adjacent tissue due to molecular excitation and generates a cylindrically symmetrical radiation pattern which encompasses and necroses the tumorous intraprostatic tissue. The necrosed intraprostatic tissue is subsequently reabsorbed by the body, thereby relieving an individual from the systems of BPH.
One method of microwave thermal therapy described in the art includes intrarectal insertion of a microwave antenna-containing applicator. Heat generated by the antenna's electromagnetic field is monitored by a sensor which is positioned near the prostate gland by a urethral catheter. However, due to the distance between the rectum and the tumorous prostatic tissue of the transition zone, healthy intervening tissue within the cylindrically symmetrical radiation pattern is thermally damaged in the course of the intrarectal treatment.
A safer and more effective treatment of BPH is transurethral microwave thermal therapy. This method of treatment minimizes the distance between a microwave antenna-carrying applicator and the transition zone of the prostate by positioning a Foley-type catheter-bearing applicator adjacent to the prostate gland within the urethra. Due to the close proximity of the microwave antenna to the prostate, a lesser volume of healthy tissue is exposed to the cylindrically symmetrical radiation pattern generated by the microwave antenna. Therefore, the amount of healthy tissue necrosed is reduced. Transurethral applicators of the type described can be found in the previously mentioned co-pending applications.
While transurethral microwave thermal therapy reduces the distance between a microwave antenna-carrying applicator and the transition zone of the prostate gland, there is still concern that healthy tissue located between the applicator and the prostate gland may be thermally damaged. In particular, it is important that the urethral wall adjacent the applicator, which is healthy, normal tissue, not be necrosed.